Commitments and Contingencies - Off-balance Sheet Financial Instruments (Detail) $ in Thousands	Dec. 31, 2020 USD ($)
Commitments to Extend Credit [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Off-balance sheet risks, amount, liability	$ 1,443,141
Performance Letters Of Credit [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Off-balance sheet risks, amount, liability	34,215
Standby Letters of Credit [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Off-balance sheet risks, amount, liability	35,998
Other Letters Of Credit [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Off-balance sheet risks, amount, liability	$ 337